Low temperature zero-level packaging of MEMS

Zero-level packaging technology ensures dicing and handling compatibility of the MEMS device along with low cost by encapsulating the MEMS components using wafer level processing. It is also essential for providing the MEMS with a controlled ambient in a cost-effective way. In order to be compatible with a broad range of MEMS processes, IMEC developed sealing methods with a low temperature budget. Zero-level packaging consists of die-to-wafer or wafer-to-wafer capping using a solder or polymer sealing. The first method is based on the soldering of e.g. SnPb. The second method uses photosensitive BenzoCycloButene as a sealing material. In order to reduce the total thickness of the package, the capping wafer can be thinned. In the “thin film capping” technology, a cap is realized using the deposition of poly-SiGe on top of a sacrificial layer. After etching of access holes, the sacrificial layer is etched. Finally the access holes are closed using an appropriate thin film sealing process. Infrared microbolometers, RF-MEMS switches and other MEMS devices have been capped. The quality of the resulting MEMS zero-level packages is evaluated using shear testing, different leak test methods, outgassing analysis as well as measuring the MEMS device characteristics.